This PDF file contains the editorial “International Year of Light” for OE Vol. 54 Issue 02

A study for the incidence geometry to extend the accepted incidence position is presented and demonstrated. High-speed and high-quality self-pumped phase conjugate mirrors (SPPCM) can be formed with a counter-direction incidence with respect to the master light for the Cat-SPPCM. In addition to a counter-directional Kitty-SPPCM, when the incidence position is changed, a Kitty-SPPCM with high-pass filtering and a different SPPCM similar to the Bridge-SPPCM can be found. The discovery of these three kinds of optical phase conjugators extends the accepted incidence position range and angle, helpful for applying the SPPCM in various new applications.

In certain imaging applications, conventional lens technology is constrained by the lack of materials which can effectively focus the radiation within a reasonable weight and volume. One solution is to use coded apertures—opaque plates perforated with multiple pinhole-like openings. If the openings are arranged in an appropriate pattern, then the images can be decoded and a clear image computed. Recently, computational imaging and the search for a means of producing programmable software-defined optics have revived interest in coded apertures. The former state-of-the-art masks, modified uniformly redundant arrays (MURAs), are effective for compact objects against uniform backgrounds, but have substantial drawbacks for extended scenes: (1) MURAs present an inherently ill-posed inversion problem that is unmanageable for large images, and (2) they are susceptible to diffraction: a diffracted MURA is no longer a MURA. We present a new class of coded apertures, separable Doubly-Toeplitz masks, which are efficiently decodable even for very large images—orders of magnitude faster than MURAs, and which remain decodable when diffracted. We implemented the masks using programmable spatial-light-modulators. Imaging experiments confirmed the effectiveness of separable Doubly-Toeplitz masks—images collected in natural light of extended outdoor scenes are rendered clearly.

Fluorescence microscopic image three-dimensional (3-D) reconstruction is a challenging topic in image processing and computer vision, and can be widely applied to life science, biology, and medicine. A microscopic images 3-D reconstruction method is proposed for transparent or partially transparent microscopic samples, which is based on the Taylor expansion theorem and polynomial fitting. First, the image stack of the specimen is divided into several groups in an overlapping or nonoverlapping way along the optical axis, and the first image of every group is regarded as the reference image. Then, different order intensity derivatives are calculated using all the images of every group and a polynomial fitting method. Subsequently, a new image can be generated by means of Taylor expansion theorem and the calculated different order intensity derivatives and for which the distance to the reference image is Δz along the optical axis. Finally, the microscopic specimen can be reconstructed in 3-D form using deconvolution technology and all the images including both the observed and the generated images. The experimental results show the superior performance via processing simulated and real fluorescence microscopic degraded images.

Night vision equipment is crucial in order to accomplish supremacy and safety of the troops on the battlefield. Evidently, system integrators, ministry of defenses and end-users need access to reliable quantitative characterization of the expected field performance when using night vision equipment. The image intensifier tube is one of the most important engines driving the performance for night vision equipment. As a major tube manufacturer, Photonis investigates the link between its products’ physical design parameters and the actual end-user field performance. The developments include (1) an end-to-end performance measurement method and test facility, (2) an image-based night vision simulation, and (3) a range estimation model. The purpose is twofold: (1) being able to support the need of the integrators and end-users and (2) further systematic improvement of night vision equipment design. For the end-to-end test, Photonis and TNO cooperated in the implementation of the triangle orientation discrimination (TOD) test for night vision equipment. This test provides a clear and rigorous ranking of the products with respect to their target acquisition performance level. We present the Photonis night vision test laboratory, provide TOD results for a set of night vision devices, and show range prediction examples.

The extensive application of surface mount technology requires various measurement methods to evaluate the printed circuit board (PCB), and visual inspection is one critical method. The local oversaturation, arising from the nonconsistent reflectivity of the PCB surface, will lead to an erroneous result. This paper presents a study on a high dynamic range image (HDRI) acquisition system which can capture HDRIs with less local oversaturation. The HDRI system is composed of the liquid crystal on silicon (LCoS) and charge-coupled diode (CCD) sensor. In this system, the LCoS uses a negative feedback to extend the dynamic range of the system, and the proportion integration differentiation (PID) theory is used to control the system for its rapidity. The input of the PID controller is images captured by the CCD sensor and the output is the LCoS mask, which controls the LCoS’s reflectivity. The significant characteristics of our method are that the PID control can adjust the image brightness pixel to pixel and the feedback procedure is accomplished by the computer in less time than the traditional method. Experimental results demonstrate that the system could capture HDRIs with less local oversaturation.

We propose a real-time line matching method for stereo systems. To achieve real-time performance while retaining a high level of matching precision, we first propose a nonparametric transform to represent the spatial relations between neighboring lines and nearby textures as a binary stream. Since the length of a line can vary across images, the matching costs between lines are computed within an overlap area (OA) based on the binary stream. The OA is determined for each line pair by employing the properties of a rectified image pair. Finally, the line correspondence is determined using a winner-takes-all method with a left-right consistency check. To reduce the computational time requirements further, we filter out unreliable matching candidates in advance based on their rectification properties. The performance of the proposed method was compared with state-of-the-art methods in terms of the computational time, matching precision, and recall. The proposed method required 47 ms to match lines from an image pair in the KITTI dataset with an average precision of 95%. We also verified the proposed method under image blur, illumination variation, and viewpoint changes.

We propose an overdrive (OD) technology to precisely compensate for the temperature-dependent response characteristics of liquid-crystal displays (LCDs). The optical responses of LCDs are highly dependent on ambient temperature. After analyzing the optimized OD values, the new OD technology uses simple calculation logic instead of bulky OD lookup tables to obtain OD values of rising transitions over a wide range of ambient temperatures. We also show that it is possible to automatically adjust the optimum OD values depending on the ambient temperature. The results show that the proposed OD technology can improve motion image quality without any motion artifacts regardless of the ambient temperature. We expect that our proposed OD technology will ensure that LCD products have a consistent motion image quality regardless of the ambient temperature without any increase in cost.

In using a fly cutter to machine potassium dihydrogen phosphate (KDP) crystals, rippling in machined surfaces will remain that will have a significant impact on the optical performance. An analysis of these low-spatial frequency ripples is presented and its influence on the root-mean-squared gradient (GRMS) of the wavefront discussed. A frequency analysis of the machined KDP crystal surfaces is performed using wavelet transform and power spectral density methods. Based on a classification of the time frequencies for these macroripples, the multimode vibration of the machine tool is found to be the main reason surface ripples are produced. Improvements in the machine design parameters are proposed to limit such effects on the wavefront performance of the KDP crystal.

In the measurement of deformation of buckling phenomenon, the optical measurement methods have been traditionally employed for performing noncontact measurement. Furthermore, because the in-plane and out-of-plane deformations simultaneously happen in the buckling phenomena, these in-plane and out-of-plane deformations must be separated precisely by analyzing some measured results of dynamic events. In traditional methods, some two-beam interferometers have been combined to measure in-plane and out-of-plane deformations as three-dimensional deformations. An ordinary two-beam interferometer is defined as the optical system that is combined by two independent interferometers. Under this definition, a new interferometer that is set up by two cameras and one laser is constructed by using the idea of a speckle interferometer that uses only two speckle patterns. Then, an analysis method for separation of in-plane and out-of-plane deformations is also proposed. In the experimental results, the high measuring accuracy of the proposed methods is confirmed. Consequently, the independency between in-plane and out-of-plane measurements in this method is confirmed. Furthermore, the new method is applied to the analysis of the buckling phenomenon. As the results, it can be confirmed that the results of the beam of buckling analysis agree very well with the theory of Euler’s buckling.

Currently, phase-shifting interferometry is widely used in MEMS (micro-electro-mechanical system) microsurface topography measurements, and an expensive and high-precision piezoelectric transducer (PZT) is often necessary to realize phase-shift operation. Because of the feature of a MEMS structure which always has a flat substrate, a practical algorithm to calculate phase shifts by fast Fourier transformation (FFT) from gathered interference fringes of the substrate is presented, then microsurface topography can be reconstructed according to the obtained phase shifts. By means of the presented algorithm, an expensive and high-precision PZT is unnecessary and the phase-shift operation can even be carried out by rotating the fine focus adjustment knob. The accuracy and feasibility of the method have been verified by experiments. Experiments indicated that the presented method can satisfy the needs of in situ MEMS topography measurements and is very simple.

Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory, several functions can be combined, the efficiency is reduced with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1  μm limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. Two different techniques, namely, a modulo-2π phase addition technique and an analog technique for design and fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented. In order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases.

Through theoretical analysis, we have previously proposed a method to measure an isoplanatic angle over a finite distance using three receiver apertures and a synthetic point source. Here, we present the validation experiment for this method. Through careful experimental design, the atmospheric coherence length for spherical waves propagating in the opposite direction was measured and converted to an isoplanatic angle as the true value for comparison. In general, the direct measurement of an isoplanatic angle agrees well with the true value in clear-air periods. Experimental results confirm our method for measuring an isoplanatic angle over a finite distance. The experiment resulted in the first time-diagram of an isoplanatic angle in finite distance ever measured through spherical-wave scintillation.

In this paper, we propose a method to detect the valid phase pixels of fringe patterns obtained with phase shifting interferometry. From a set of simulated interferogram images, we obtain a set of equations to discriminate between valid and invalid wavefront phase pixels, which allow us to compute the wavefront aberration. This method is useful for testing any converging optical system in a quantitative way with either a small or large focal ratio, with either polished or rough surfaces and with wavefront or lateral shear interferograms.

We present a study on spatial changes in the accuracy of tomographic reconstructions obtained with two of the most popular tomographic reconstruction algorithms for diffraction tomography—filtered backprojection (FBPJ) and Rytov-based filtered backpropagation (FBPP). We find out that not only FBPJ but also FBPP suffers from a significant loss of accuracy in the off-axis regions of a tomographic reconstruction and this effect is stronger for objects with a high refractive index contrast. Moreover, we propose some modifications to FBPP which allow for significant improvement of the off-axis performance of the algorithm. In the modified algorithm, called the extended depth of focus filtered backpropagation (EDOF-FBPP), scattered waves are backpropagated using a rigorous propagation algorithm, and then the Rytov approximation is applied on extended EDOF images. This modification (1) prevents violation of the Rytov validity condition due to the defocus of scattered waves and (2) suppresses unwrapping errors. The tomographic reconstruction algorithms FBPJ, FBPP, and EDOF-FBPP are extensively tested with numerical simulations supported with rigorous wave scattering methods. The experimental evaluation of the performance of the tomographic algorithms is provided with a tomographic measurement of an optical microtip located 21 μm from the central axis of the reconstruction.

A reference differential detection method (RDDM) for micrograting accelerometers is described to suppress laser relative intensity noise (RIN). A three orders-differential scheme and reference detection method are combined to complement the output and to reduce the background light interference. A theoretical model of RDDM to suppress RIN is established and analyzed based on the scalar diffraction theory. Then the reference differential detection circuit (RDDC) parameters are designed to achieve the optimal sensitivity for the accelerometer based on the model. Experimental results indicate the sensitivity of the micrograting accelerometer is 2.22  V/g. The overall signal-to-noise ratio of this method is improved by 7.3 dB at 100 Hz and the noise level is obviously reduced compared with that of the device without RDDM.

Spin-coating provides a facile method for the production of highly uniform thin films that have applications as photoresists, coatings, and in organic electronics. Due to the rapid high-speed nature of spin-coating, obtaining data in situ has proved problematic. Recently, a number of in situ characterization techniques have provided new insights into the processes occurring during spin-coating. This paper demonstrates a straightforward method for obtaining in situ optical reflectance images during spin-coating that provide insights into film thinning dynamics, the origins of surface inhomogeneities caused by contaminated substrates, and crystallization processes. This technique could be easily implemented industrially and in many laboratories and will allow for a better understanding of the spin-coating process.

In this publication, we give a brief introduction into the field of computational shear interferometry, which allows for determining arbitrary wave fields from a set of shear interferograms. We discuss limitations of the method with respect to the coherence of the underlying wave field and present various numerical methods to recover it from its sheared representations. Finally, we show experimental results on digital holography of objects with rough surfaces using a fiber coupled light-emitting diode and quantitative phase contrast imaging as well as numerical refocusing in differential interference contrast microscopy.

We recently reported on a mathematical formalism for analyzing the result of a direct-write scanning system applied to photoaligned liquid crystal films. We use that formalism to study the direct-write recording of polarization gratings (PGs). First, we evaluate three scan paths in simulation and experiment, describe their tradeoffs and practical constraints, and identify the most favorable. Second, we explore the parameter space of direct-write PGs in simulation, which includes four dimensions in general: grating period, line spacing, beam size, and spatially averaged fluence. Using this analysis, we predict that a certain portion of the parameter space should be optimal, leading to high diffraction efficiency and well-aligned PGs. Finally, we experimentally fabricate and characterize nine PGs with scan parameters within and around this optimal parameter space and conclude that the prediction is validated. This work is the first in-depth study of direct-write PGs; it identifies many challenges and solutions, and shows, for the first time, direct-write recorded PGs with quality equivalent to those recorded via holography. In particular, we demonstrate a PG (20  μm period) with first-order diffraction efficiency 99.5%, 0.2% haze, and polarization contrast of 2000.

Improving the coupling efficiency of tapered metallic gaps using spatial amplitude modulation is theoretically investigated. The influences of the critical parameters on the coupling efficiency, such as incident beam width, incident wavelength, and numerical aperture of coupling lens, are analyzed, respectively, and a coupling efficiency increase of about 16.43-fold is obtained by optimizing these parameters. The physical mechanism of the coupling efficiency improvement is further discussed. The substantial improvement of the coupling efficiency via spatial amplitude modulation shows the potential in designing tapered metal-insulator-metal waveguides for field enhancement and nanofocusing.

In recent years, optical zoom imaging without moving elements has received much attention. The key to realizing this technique lies in the design of the variable-curvature mirror (VCM). To obtain enough optical magnification, the VCM should be able to change its radius of curvature over a wide range. In other words, the VCM must be able to provide a large sagittal variation, which requires the mirror material to be robust during curvature variation, require little force to deform, and have high ultimate strength. Carbon-fiber-reinforced polymer (CFRP) satisfies all these requirements and is suitable for fabricating such a VCM. Therefore, in this research, a CFRP prototype VCM has been designed, fabricated, and tested. With a diameter of 100 mm, a thickness of 2 mm, and an initial radius of curvature of 1740 mm, this VCM can provide a maximum 23-μm sagittal variation and a minimum and maximum radius of curvature of 1705 and 1760 mm.

We describe a simple but very efficient optical device that allows the dynamic focusing of unpolarized light using a single-nematic liquid crystal layer. The operation principle of the proposed device is based on the combination of an electrically variable “half-lens” with two fixed optical elements for light reflection and a 90-deg polarization flip. Such an approach is made possible thanks to the close integration of the thin film wave plate and mirror. Preliminary experimental studies of the obtained electrically variable mirror show very promising results.

High birefringence and large mode area are the two paramount requirements of single-mode fibers to control polarization mode dispersion and nonlinear effects. We have investigated the birefringence, higher-order mode coupling loss of a fundamental mode (FM), and numerical aperture of index-guiding segmented cladding photonic crystal fibers in continuation to our previous analysis of the design for FM confinement and V parameter. High birefringence on the order of 10⁻⁴ to 10⁻³ over the near-infrared to short-wavelength infrared (0.75 to 2.3  μm) spectral range has been obtained. The finite difference time domain method has been used for simulation. The center defect in the lattice forms the core and the remaining part represents the cladding. With phosphate glass (n_gl=1.56) as a base material, cladding consists of different segments formed by varying the air hole diameter resulting in strong form birefringence and reduced numerical aperture which leads to a large mode area. We inferred a relation between fiber symmetry and birefringence by varying the duty cycle of the designs. A significant reduction in beat lengths shows reduced power losses in the FM due to higher-order mode coupling.

Peripheral refraction, the refractive error present outside the main direction of gaze, has lately attracted interest due to its alleged relationship with the progression of myopia. The ray tracing procedures involved in its calculation need to follow an approach different from those used in conventional ophthalmic lens design, where refractive errors are compensated only in the main direction of gaze. We present a methodology for the evaluation of the peripheral refractive error in ophthalmic lenses, adapting the conventional generalized ray tracing approach to the requirements of the evaluation of peripheral refraction. The nodal point of the eye and a retinal conjugate surface will be used to evaluate the three-dimensional distribution of refractive error around the fovea. The proposed approach enables us to calculate the three-dimensional peripheral refraction induced by any ophthalmic lens at any direction of gaze and to personalize the lens design to the requirements of the user. The complete evaluation process for a given user prescribed with a −5.76D ophthalmic lens for foveal vision is detailed, and comparative results obtained when the geometry of the lens is modified and when the central refractive error is over- or undercorrected. The methodology is also applied for an emmetropic eye to show its application for refractive errors other than myopia.

Automatic optimization algorithms have been recently introduced as nonimaging optics design techniques. Unlike optimization of imaging systems, nonsequential ray tracing simulations and complex noncentered systems design must be considered, adding complexity to the problem. The merit function is a key element in the automatic optimization algorithm; nevertheless, the selection of each objective’s weight, {w_i}, inside the merit function needs a prior trial and error process for each optimization. The problem then is to determine appropriate weights’ values for each objective. We propose a new dynamic merit function with variable weight factors {w_i(n)}. The proposed algorithm automatically adapts weight factors during the evolution of the optimization process. This dynamic merit function avoids the previous trial and error procedure by selecting the right merit function and provides better results than conventional merit functions.

In the early 1990s, Church and Takacs pointed out that the specification of surface figure and finish of x-ray mirrors must be based on their performance in the beamline optical system. We demonstrate the limitations of specification, characterization, and performance evaluation based on conventional statistical approaches, including root-mean-square roughness and residual slope variation, evaluated over spatial frequency bandwidths that are system specific, and a more refined description of the surface morphology based on the power spectral density distribution. We show that these limitations are fatal, especially in the case of highly collimated coherent x-ray beams, like beams from x-ray free electron lasers (XFELs). The limitations arise due to the deterministic character of the surface profile data for a definite mirror, while the specific correlation properties of the surface are essential for the performance of the entire x-ray optical system. As a possible way to overcome the problem, we treat a method, suggested by Yashchuk and Yashchuk in 2012, based on an autoregressive moving average modeling of the slope measurements with a limited number of parameters. The effectiveness of the approach is demonstrated with an example specific to the x-ray optical systems under design at the European XFEL.

A method for joint transmission line and aperture field integration (TL-AFIM) is proposed and utilized to efficiently compute the near-field distribution of the finite-sized multilayered dielectric plates. Four indicators E_pv, E_rms, φ_pv, and φ_rms representing the amplitude and phase variations are proposed to evaluate the near-field uniformity. A multilayered dielectric plate containing three dielectric layers is analyzed and evaluated by TL-AFIM. Compared to the commonly used multilevel fast multipole method (MLFMM), the memory requirement and CPU time consumption are drastically reduced from 61.3 GB and 20.2 h to 4.4 MB and 2.5 s, respectively. The calculation accuracy is better than 90%.

A compact two-dimensional laser scanner based on piezoelectric actuators is presented. The scanner consists of two single-axis laser scanners placed perpendicular to each other, which exhibit the advantages of small size, large angle, high scanning speed, and high linearity. The mechanical structure and principle of the scanner are introduced and the performance of the scanner is experimentally investigated. The result shows that the maximum angle of the scanner is approximately 9.315 deg with a main resonant frequency of 1242 Hz. An open-loop controller based on a hysteresis compensation algorithm and analog notch filter is proposed. Its nonlinearity is reduced to ±0.5% after compensation. High frequency scanning and the step response of the scanner are also studied to demonstrate the performance and effectiveness of the scanner.

Deflectometry is a powerful metrology technique that uses off-the-shelf equipment to achieve nanometer-level accuracy surface measurements. However, there is no portable device to quickly measure eyeglasses, lenses, or mirrors. We present an entirely portable new deflectometry technique that runs on any Android™ smartphone with a front-facing camera. Our technique overcomes some specific issues of portable devices like screen nonlinearity and automatic gain control. We demonstrate our application by measuring an amateur telescope mirror and simulating a measurement of the faulty Hubble Space Telescope primary mirror. Our technique can, in less than 1 min, measure surface errors with accuracy up to 50 nm RMS, simply using a smartphone.

This paper suggests an optical printed circuit board (OPCB) having new optical coupling structures, including a laser-drilled and under-filled structure (LD-UFS) and a vertical waveguide structure (VWS). The suggested OPCB has the features of high-speed data transmission as well as highly efficient optical coupling because it was fabricated with low-dielectric and transparent electrical PCB materials through a PCB compatible process. To evaluate and compare the optical and electrical performances of the suggested OPCB with those of other OPCBs, the various types of OPCBs were fabricated and measured. The optical coupling losses of the LD-UFS and the VWS were measured with excellent results of 9.8 and 7.8 dB, respectively, which are lower than that of the basic structure. The electrical 3-dB bandwidth of the OPCB was also evaluated up to more than 40 GHz.

Freeform surfaces enable imaginative optics by providing abundant degrees of freedom for an optical designer as compared to spherical surfaces. An off-axis two-mirror–based telescope design is presented, in which the primary mirror is a concave prolate spheroid and the secondary mirror is freeform surface-based. The off-axis configuration is employed here for removing the central obscuration problem which otherwise limits the central maxima in the point spread function. In this proposed design, an extended X−Y polynomial is used as a surface descriptor for the off-axis segment of the secondary mirror. The coefficients of this extended polynomial are directly related to the Seidel aberrations, and are thus optimized here for a better control of asymmetric optical aberrations at various field points. For this design, the aperture stop is located 500 mm before the primary mirror and the entrance pupil diameter is kept as 80 mm. The effective focal length is 439 mm and covers a full field of view of 2 deg. The image quality obtained here is near diffraction limited which can be inferred from metrics such as the spot diagram and modulation transfer function.

It is desirable to engineer a small camera with a wide field of view (FOV) because of current developments in the field of wearable cameras and computing products, such as action cameras and Google Glass. However, typical approaches for achieving wide FOV, such as attaching a fisheye lens and convex mirrors, require a trade-off between optics size and the FOV. We propose camera optics that achieve a wide FOV, and are at the same time small and lightweight. The proposed optics are a completely lensless and catoptric design. They contain four mirrors, two for wide viewing, and two for focusing the image on the camera sensor. The proposed optics are simple and can be simply miniaturized, since we use only mirrors for the proposed optics and the optics are not susceptible to chromatic aberration. We have implemented the prototype optics of our lensless concept. We have attached the optics to commercial charge-coupled device/complementary metal oxide semiconductor cameras and conducted experiments to evaluate the feasibility of our proposed optics.

The Dragonfly directional sensor was deployed at the Army’s Yuma Proving Grounds for preliminary field tests against rocket-propelled grenades. This wide-field (nonimaging) sensor’s purpose was to angularly locate the latter’s launch plume. These tests successfully demonstrated proof-of-concept.

To achieve a full-aperture, diffraction-limited image, a telescope’s segmented primary mirror must be properly phased. Furthermore, it is crucial to detect the piston errors between individual segments with high accuracy. Based on the diffraction imaging theory, the symmetrically shaped aperture with an arbitrarily positioned entrance pupil would focus at the optical axis with a symmetrical diffraction pattern. By selecting a single mirror as a reference mirror and regarding the diffraction image’s center as the calibration point, a function can be derived that expresses the relationship between the piston error and the distance from the center of the inference image to the calibration point is linearity within one-half wavelength. These theoretical results are shown to be consistent with the results of a numerical simulation. Using this method, not only the piston error, but also the tip–tilt error can be detected. This method is simple and effective; it yields high-accuracy measurements and requires less computation time.

A full-duplex fiber-wireless link with a uniform single sideband differential quaternary phase-shift keying optical millimeter-wave signal is proposed to provide wired or 40-GHz band wireless access alternatively. The uniform optical millimeter-wave signal that supports services for wired or wireless users is produced via an LiNbO₃ Mach-Zehnder modulator. After being transmitted to the hybrid optical network unit (HONU), it can be demodulated in different patterns on the demand of the user terminals for wired or wireless access. Simultaneously, part of the blank optical carrier abstracted from it is reused as the uplink optical carrier, so the HONU is free from the laser source, and thus, the complexity and cost of the system are reduced. Moreover, since the two tones of the dual-tone optical millimeter wave come from the same source, they maintain high coherency even after being transmitted over fiber. Additionally, the downlink data are carried by one tone of the dual-tone optical millimeter wave, so the downlink optical millimeter-wave signal suffers little from the fiber chromatic dispersion and laser phase noise. The theoretical analysis and simulation results show that our proposed full-duplex link for alternative wired and wireless access maintains good performance even when the transmission link with standard single mode fiber is extended to 30 km.

We report a hybrid integrated external cavity laser by butt coupling a quantum dot reflective semiconductor optical amplifier and a silicon-on-insulator chip. The device lasers at 1302 nm in the O-band, a wavelength regime critical to data communication systems. We measured 18 mW on-chip output power and over 50-dB side-mode suppression ratio. We also demonstrated open eye diagrams at 10 and 40  Gb/s.

Uniform near-infrared (NIR) and short-wave infrared (SWIR) illuminators are desired in low ambient light detection, recognition, and identification of military applications. Factors that contribute to laser illumination image degradation are high frequency, coherent laser speckle and low frequency nonuniformities created by the laser or external laser cavity optics. Laser speckle analysis and beam uniformity improvements have been independently studied by numerous authors, but analysis to separate these two effects from a single measurement technique has not been published. In this study, profiles of compact, diode laser NIR and SWIR illuminators were measured and evaluated. Digital 12-bit images were recorded with a flat-field calibrated InGaAs camera with measurements at F/1.4 and F/16. Separating beam uniformity components from laser speckle was approximated by filtering the original image. The goal of this paper is to identify and quantify the beam quality variation of illumination prototypes, draw awareness to its impact on range performance modeling, and develop measurement techniques and methodologies for military, industry, and vendors of active sources.

A rotational-angle sensor composed of two Fiber Bragg gratings glued axially on a cylindrical cantilever beam to be bent by the resultant repulsion force of three magnets is designed and proposed for detecting the rotary random position of a rotor. By means of using three different materials on cantilever beams for checking each feature’s effect on this fiber optic sensor, it has been experimentally confirmed that a nearly identical performance is achieved among them. From these experimental results, a maximum deviation of 1.3 deg is obtained and it is in good agreement with the theoretical prediction. As a whole, the cantilever design exploited in this proposed optical fiber sensor configuration is independent of the intrinsic materials used. This sensor can provide a robust kind of technique for accurately measuring the rotational angle or rotational rate of a rotor in an arbitrary rotational direction for a wide range of industrial applications.

A high-sensitivity temperature sensor based on optical fiber delay is proposed in this paper. The sensor system is designed and tested in a temperature range of 0°C to 100°C with increments of 5°C. The output delay difference is found to be linearly proportional to the temperature with an average fluctuation less than 0.1 ps. To achieve an overall low cost and practical detection, a simple detection system is developed to measure temperature, and a potential for high temperature sensitivity is shown by analyzing the system. As a result, this sensor system is proven to be feasible and practical, and temperature can be measured in a simple and economical way.

We propose and analyze a frequency 32-tupling scheme which is capable of generating millimeter and terahertz waves without being affected by the phase noise difference between two incoherent sources. In our work, the process of the optical sidebands’ phase noise change is theoretically analyzed and confirmed by simulations. In addition, the system performance in terms of linewidth, tunability, and stability is also investigated.

Fluorescent optical fibers are used in nuclear detection and other forms of fiber-optic sensors. The trapping efficiency of a fluorescent optical fiber is defined by the optical energy trapped (or guided) by the fiber divided by the total energy emitted within it by the fluorescers that dope the fiber core. This characteristic is clearly important in determining the size of signals from these devices. A calculation of the trapping efficiency has been performed under the assumption that the fluorescence radiation is emitted isotropically by the individual fluorescers that are uniformly distributed throughout the core and are equally likely to be excited by particles or shorter-wavelength light. At the price of increased complexity, nothing in the analysis precludes the lifting of these restrictions. What is included in this analysis is the contribution of skew rays, which, to the author’s knowledge, is not presented elsewhere. A very simple expression for the trapping efficiency as a function of the cladding-to-core index ratio is derived. Also important in determining signal size is the transmission loss of the fluorescence radiation to either end of the fiber from the point of its generation. However, as it is a separate matter, it is not discussed here.